Current motors



Oct. 30, 1928. 1,689,559

B. RAETTIG AUTOMATIC STARTING DEVICE FOR ALTERNATE CURRENT MOTORS Filed Feb. 9, 1926 2 Sheets-Sheet 1 3 a c .h

6 AIBLQE'L Robb a'irulion of Start I. dltd "eil ad 1 KW a m: a (fluid: o J 4 Entry of slip M ir A2 upby U1: star!" A; M starting Juice h mechanical g: cfficiznz, a the molar on 4 darling synchronous 0 4 p n 2 Jircklian of afar! IIIWWI Hg. 5; F1256 6 Oct. 30, 1928. 1,689,559

B. RAETTIG AUTOMATIC STARTING DEVICE FOR ALTERNATE CURRENT MOTORS Filed Feb. 9, 1926 2 Sheets-Sheet 2 i; I; 1| 1; I! I: I I l- 1: I I I f fl// 70 0J E H l 1; u l I H :l I 1: I: ll h l I b 5 .4 5 29- sr4m/a- I I] H H- II j R am I u u H I 17 van for:

Bruno Fae/# V 5 PM Patented Oct. 30, 1928.

warren STATES PATENT OFFlCE.

BRUNO 'RAETTIG, OF HOFFNUNGSTHAL, NEAR COLOGNE, GERMANY.

AUTOMATIC STARTING DEVICE FOR ALTERNATE-CURRENT MOTORS.

Application filed February 9, 1926, Serial No. 87,118, and in Germany January 13, 1925.

This invention relates to automatic starting means for alternating current motors and particularly three-phase motors 'in which choke coils with magnetizable and preferably closed, yoke-shaped cores are connected in series .with the rotor winding of the motor. Choke coils of the kind referred to set. up a counter-electromotive force in i the starting of the motor which is; opposed to 10 the rotor voltage generated by the slip in the rotor. Both arm-alternating current electromotive forces or voltages the magnitude and frequency of which 1 are proportional to the slip.- Y

l5 With the motor would not; Edevelop any starting torqueeand in .o'rder-to produce such a startingfitorqu, it is'snecessaryto overcome the secondary current. This is effected by'the emplo ment of-a magnetizable, close-d, yokeshape =core.-- -;.'As heretofore. const or'wit-h a uniformly: laminated; core of the the slippingten'erg y. With: the-use of. a core solid either throughout its length-,onthrough.

- parts -ofhitsringtli, ritlieulossessi from? Leddy;

oi different thickness were tobe foundin a,

T currents? are proportionah to: the square of the frequency. Since a. constant starting- .torque,: however;::requ1res,=a :straight line -+curve: Motors with the use of solidcores are reduced: to approximately 1 halt-the propvr numberof rotations t lm the case of high frequencies cores 'w1th what is known is implied by the phrase:

will prevent :the passage of any appreciable 40 ii'rthe starting operation-which reduces the "starting torquefand the starting'current is accordingly undesirably high. Y In the second case, that :is 'to say, wlth the use-of a uniformly-laminated:core, the generatedvoltageor line drop is proportional,

to; the frequency, so as to again result in losses approximating the square of. the frequency. The-starting of a motor of the kind referred-to will therefore take place substantially as follows z- The first current impulse being large, due to the high losses,' the motor start with a jerk'and'onlyrun at ap roximately half the desired number 1% revolutions at aht' iit use of: the choke coils only, the

ructed, choke coil's of th-is kind were provided with a solid core field. In consequence thereof an excessively high difference of phaseire'lation will-occur curve of a quadratic equation representing,

quency, that is to say, when the slip has arrwed at a high .value in accordance with my invention. For this purpose the core may be differently laminated at difl'erent points of itsecross section,..a nd in such a manner that thenon-laminatedpathfor the lines of force will be suflicient for low frequencies. while the highly laminated path of the lines of force will have to; haemployed with high frequencies,-eitlier alone or in combination with the employment of the less laminated section. Laminating the iron cores of choking coils-is, welliknown.

Likewise i to make the .core or aicrtain length of thinner plates and the othe r part of its length of thickersplates so that -the lines of force pass on their path successively through thicker andthinner plates is well knownq It, was, however notknowntolam- ,inate .thej core-in ,such a manner that plates of the cross-sectional area of weaker or-thinner plates. -;This difi'erence as, compared ,laminated differently in different places-of its cross-sectional area. By} this means, the

the losses from eddy currentis changedt-o .aistiaight line,iinasmuch as with high;-fr.e-

quency the lines of force will be directed into that portion of the-corewhichis lamiznated with thin pieces, of sheet iron and which, therefore, shows only smalllosses from eddy currents, while the residue of lines of force still remaining in the portion of the cross section-of the corewhichis laminated with thicker sheets producesthe necessary losses by eddy currents, wit hout, however, allowing them to r se excessively. Upon the reduction of the f1-eque cy, the this will, howe er, preferably ears Waugh paratively greater losses by eddy currents are 'protluce d. "so as to counteract the droppingof the starting torque. By asuitahle' selection "f thematiO-of the cross sectionof the cor'and the number of windings,the'result-is producedthatthe difference of phase in the starting circuit is-oiily small'on startjing, so as to 'c ause the flowing 'of a high" "working currentwhich produces a high fThedffiernFkinds off la'in'inations, in acstartingto'rque with low current.

" cfordane withfthisinvention, will, moreover; resultf'ilfan extraordinarily intensi- -'fied formatiomotf the eddy' currents, which I adapted-to produce torque: This :condiis anesthes a-the case Io solid core" ""5 'lth, a""v'ie'w of increasingthe starting =torgu*,'- Hume keeping the 'mass; of the core a ti'ons will he suchthatthe-slip voltage-nec- "essary 'for the current'fiow will be-produced ma be'proi 'ided {inth'e' well known fni anner, vyhichfin accordance with this inwen-ties; will {show approfimately straight {line "increasing 'losse",so "f -g'en'er'gy. For this lliind dfsecondary'coils the mostsultable are: 'coil szo fma'gnetizallle materia and of square ante 'this -ir'rventioiimayhe disposed 'on th shaft of the rotor as Mother i'll' known arrangements" and -separate" from the motor Klnithe well known niannensothat itmay mg i 'g preferred and'by way drexample- "Fig. "-1 is 'a Sketch of the electrie connections, Fig. 2 illustrates diagrammatically the pr' '"e'dure according to thi's'inventi'on. .Fig.' 3'='is a diagrammatic illilstrationcf"the'curves representing the fili fierent'torques. "Figs t, fl antl '4" illus' :er'atein plan,'-nd"and side elevations'the con- 'struetion'df an'ironc'ore;' Fi 's; 5 -and 5" are graplrs oi-diagrams of the fidld distribution. Figfi i'llustiates diagrammatically the construction of the starting device. Fig.7 is a diagram of the electrical connections with the "starting devicemounted on "the rotor shaft;

""In the sketch of electric connections, according to Fig. 1;, s s'hows'the windingofthe statonrindic-ates the rotor windin d is the Winding of the dhoke'coils, and at' lc-the sliding rings of the rotor are indicated. For clearness in illustrating the mode of operation, it may be assumed that the starting torque and the kilowat inputvimparted t0 the stator are constant in accordance with the sketch of Fig. 2. If certain input in kilowatts is admitted to the stator, this amount, aside from'the losses in 'therstator and-rotor, will have to be communicated from the rotor to 'the-startin'g'device and will be partially converted into heat in the-starting device. In the-motor a torque'is generated in proportion to the amount of input, but at this moment the motor does not produce any mechanical worlc At'the point of operation P which corresponds to a point in the starting operation the total energy admitted to the system remains unchanged. A portion is transformed into mechanical "work at unchanging torque and with the *number of' rotations '12,. The remainder A, an have-'to be converted-into =heat1in the starting device. \Vit-h synchronous numhers of revolutions all the energy taken up 'will= be transformed -into:nncchanical work, but there would be no voltage'clrop in the rotor and-no current would .flow' therein tion cannot he arrived at, but shortly before 5 this point is reached, the operating :condi- Thus,'b'esidesthe dnput kilowatt transformed into medhanica'l work N,, there is-the--re-' mainder N iiwhich urepresents the, rotor losses: In 'this "connection the stator has been assumed for simplicity ssake'to' be free sfwhich is vadmissable .=for-.pracfinal-purposes r 1 Thetra nsformati'on .into hen t above refer- 're'd to =resiilts only for :the smallest part "-frornthe heut losses of the current in the wintlings of the -rotor and :of the starting (levieefand from the hysteresis -losses -in the iron cord By farztheigreater part is transformed into heat byieddy currentsdn the i ron core. "This iron core is-not-thinly laminaitedoso as mot to-disturb the-fovmation-of the eddy currentslint it eonsists of sheets Y of 'greateri thidkness.Jilhe thickness of the :metal sheets is selected in accordance with *the particular ipurpose. {lhe :heat losses of the currents are independent -of the frequency (the slip) and thelosses-by hysteresis with different frequencies \will therefore .be

somewhat as shown bythe curve-Vdn'Fi'g. 3. 'lheret'rom thetorquealso shown an 'Elgfl3rhy the curve N is obtained which corresponds to the starting of the motor. This torque is, therefore, not at all constant, broadly considered, inasmuch as at its middle portion it shows a decided minimum. At this point the torque amounts to only about half of thetorque at the beginning of the curve.

The reduction of the initial peak of the torque may be produced by the employment of an iron core composed of metal sheets of different thickness. Such anarrangement is shown, for instance, diagrammatically in Fig. 4. In those portions of the cross section of the core which are composed of thick sheets strong eddy currents are produced with high frequencies, that is to say, with a high slip. These eddy currents prevent the increase of the field of force to its full strength, and they consequently counteract the complete-formation of the eddy currents. In the thin metal sheets, however, the field maybe completely developed, inasmuch as with this arrangement the formation of eddy currents is only :limited. In Fig. 5. the distribution 'of the-field over the cross section of athin-sheetiat 50 cycles is shown. Fig. 5 illustrates the distribution of the field in a thickmetal sheet; -With themeduction of the frequency the distribution approaches 'thedotted line of'Fig. :5 so that'the entire crosssection will: thernbe uniformly--traversed by the field' of force. It appears, therefore that the employment ofa core composed: of a combination of thick and thin sheets will produce the result thatthe curve of the eddy currentilosses does not follow thecurve of a quadratic equation, but that it will rise sfiproxfiniatl resulting in the desired curve for the torque. This procedure may be further assisted, as already mentioned, by the provision of air gaps in the thinly laminated path of the lines of force, as indicated in Fig. 4. By the arrangement of this air gap the lines with low frequencies will be compelled to flow for the most part from the thin sheets into the thick sheets which are not interrupted. With low frequencies a strong formation of eddy currents will, therefore, take place. With higher frequencies the lines of force are able to pass through the air gap, and they will then mainly flow through the thinly laminated section in View of the high resistance produced in the less laminated portion by the formation of eddy currents, so that the formation of eddy currents is comparatively small with high he quencies.

As it appears from Fig. 6, the eddy current losses may be increased by placin one or more rin s of solid metal around eac leg of the starting device, the rings being so arran ed and selected that they produce the tendency of causing the losses to become linearly increased, in consequence of the great increase of the alternating current reto a straight lines it is arrested, inasmuch as the starting de- J vice will then consume the energy .and the motor will operate merely as a transformer. If, therefore, on the occasional failing of the voltage, the motor is arrested, it will be normally started again, as soon as the voltage has increased and without requiring any manipulation or' switching of the starting device by hand., By the combinationofthe motor witha. starting device mounted on the'shaft, asshownin Fig. 7, for instance, in

placeof the sliding ringson the motor shaft and a stationary starting device, a highly perfected ideal short-circuited motor with great starting torque andlow switching current isobtained.-, eff

An advantage of this kindof starting device in connection'with the motor as described isfurther presentedby the. absolute elimination of; sparking, in view of;,t he avoid ing of the sliding; rings, sothatg-the motor is safe from .e 2 ;pl0sions and-is .wellv adapted for operation in; plants, .;with; dustyatmospheres. The employment of the start-in device, moreover, obviates the likelihoo of rotor defects, inasmuch as the line drop may be kept low in the rotor even with large wire winding.

The cooling of the starting device which, as before mentioned, is effected by a ventilator or fan action during rotation; it may also be performed with oil in the case of the separate mounting of the starting device,

I claim 1. An automatic starting device for a polyphase induction motor mounted on the rotor of said induction motor, including in combination, a closed magnetic circuit core, a winding on said core in circuit with each phase winding on the rotor of said motor, said core being composed of laminations of different thicknesses throughout its cross section whereby eddy currents are automatically decreased at high frequencies when there is a relatively large slip.

2. An automatic starting device for a polyphase induction motor mounted on the rotor shaft of said induction motor, including in combination, a closed magnetic circuit core, a winding on said core in circuit with each phase winding on the rotor of said Ian motor, said core being composedof lamina- -tions of different thicknesses throughout its cross section whereby-eddy currents-are automatically decreased at high frequencies when there is a relatively =large-slip, and a short circuited secondary winding on said core.

3. An automatic starting device for a polyphase induction motor mounted on the rotor of said induction motor, including in combination, a core having a closed magnetic circuit, a winding-on said-core in circuit with each phase windingon'the-rotor of-said motor, said-core b'e'ingcomposed of-sectional laminations of different thickness arranged throughout -its cross section, certain of said sections "being spacedto provide aii gaps in'their laminationtransverse-to the path of the magnetic flux, said gaps extending only part wvay throughout the'cross section of the core. I

4. An automatic starting device for a polypliase induction motor mounted on the rotor-shaft ofsaid induction motor, including in combination, a magnetic" circuit, a ivin'ding on said core in circuit with ea'oh' p'hase wintlingon the 'rotor 'dfsaid meted-said core blhg-COIH- posed of sectional --lamin'ations' of di'fferent thicknesses arranged throughout-its -'cross section, eer tainof said sections being spaced to provide ai'pgaps' in their laminations transverse to' thep'aith *of the magnetic flux, said gaps extendingwnly par-t way through out'the cross section-of the-com and-a short circuited secondary winding'on' said core;

automatic starti ng dafice' 'for a core having =a closed :polyphase induction motor mounted on the rotor shaft of said induction n'iotor,;including in combination, a core having :a closed magnetic circuit, a winding on said core iin circuit with each phase winding on the rotor of said motor; said core being composed of sectional laminations of diflerent thickness arranged throughout its cross section, ;certain of said sections being spaced-to provide air-gaps in their laminations transverse to it-he path ofrthermagnetic fiux, said ,gaps extending only part way throughout the cross section of the core, and one or more closed circuited secondary coilson said core, said secondary coils being :arranged to provide linearly increasing energy loss.

6. An automatic starting device ifor a polyphase induction motor mounted-on the rotor of said induction motor, including in combination, a core having a closed-magnetic circuit, a Winding on said (core in circuit with-each phase Winding omthe-rotbrvoflsaid motor, said core being composedofsectional laminations ofdifierent thicknesses arranged :throughou't its-cross section,.eer.tain :of said sections :heing spaced ito provide air-gaps in their laminations transverse :to-ithepath of the magnetic flux, said gapsextending-only apart way throughout-the :cross section 'of'the core, and one or more closed :circuitedsecondary coils of .magnetizable' :material on said core, said secondary coils being arranged to provide linearly increasing: eniergy lossr Y In testimony whereof =I. afiix'rny signature.

BRnNo RAETTIG. 

